Become a TFP Supporter Pool Math Forum Rules Pool School
Results 1 to 5 of 5

Thread: unexplained pressure drop

  1. Back To Top    #1
    iam4iam's Avatar
    Join Date
    May 2012
    Location
    Johnson City, TN
    Posts
    210

    unexplained pressure drop

    Thanks to TFP, I recently fixed an air leak which was causing a failure to prime, but now I have a new quandary, which may or may not have anything to do with my pump, which I assume is very old. Anyway, after vacuuming, as expected, filter pressure rose to the point of low return--smile if you now have a Kansas song playing in your head--about 25 PSI. Since it was getting dark, I decided to backwash the next day when I would be able to see the water viewing glass more clearly. To my surprise, the pressure the next day was less than 20 PSI. I backwashed anyway since clean pressure is well under 15 PSI and added DE, bringing my pressure to 14.5 PSI. The pool was cloudy after the first vacuum since the pool floor was pretty dirty and a lot of debris didn't make it into the vacuum and got stirred up instead. That being the case, several days later, the water was clear again and I could see I had more vacuuming to do. This time, pressure rose to about 21 PSI. Again, due to darkness, I postponed the backwash until the next day. Once again, I found the pressure to have decreased by about 5 PSI, to about 16 PSI. (It was actually initially around 15, but gradually rose to 16 during the hour or so it was on.) Also, this is somewhat subjective, but the force of water at the returns seems to be weaker than it should be with the pressure only marginally higher than right after backwashing and adding DE. (It is, at least, noticeably stronger at the returns than it was at 21 PSI before I turned off the pump right after vacuuming.) This seems very strange. Is the debris on the surface of the sand doing some sort of settling when the pump is off to cause this decrease in pressure? Ciould it have anything to do with the old pump? Thanks in advance for any ideas.
    ~18,000 gal (16x32)
    Hayward sand filter
    Circupool RJ45 SWG
    Hayward Max-Flo XL SP2305X7 pump (0.75 HP)

  2. Back To Top    #2

    In the Industry

    duraleigh's Avatar
    Join Date
    Apr 2007
    Location
    Sebring, Florida
    Posts
    30,084

    Re: unexplained pressure drop

    Is the debris on the surface of the sand doing some sort of settling when the pump is off to cause this decrease in pressure?
    That's pretty close. When the pump shuts off and turns on, there is disturbance in the sand bed that typically stirs up the tightly packed dirt and allows more water flow....hence, lower pressure, but only for a while.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  3. Back To Top    #3
    iam4iam's Avatar
    Join Date
    May 2012
    Location
    Johnson City, TN
    Posts
    210

    Re: unexplained pressure drop

    Thanks, Dave. So I guess I should expect to have to backwash again soon, then.
    ~18,000 gal (16x32)
    Hayward sand filter
    Circupool RJ45 SWG
    Hayward Max-Flo XL SP2305X7 pump (0.75 HP)

  4. Back To Top    #4
    Mod Squad jblizzle's Avatar
    Join Date
    May 2010
    Location
    Tucson, AZ
    Posts
    37,389

    Re: unexplained pressure drop

    You should backwash when the pressure rises 20-25% over your clean pressure.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
    500 sqft Heliocol solar panels, ThePoolCleaner, TF-100 test kit w/ SpeedStir
    Pool School + Test Kit + PoolMath = A TROUBLE FREE POOL
    If you found TFP helpful and we saved you money ... Become a TFP Supporter!

  5. Back To Top    #5
    iam4iam's Avatar
    Join Date
    May 2012
    Location
    Johnson City, TN
    Posts
    210

    Re: unexplained pressure drop

    You should backwash when the pressure rises 20-25% over your clean pressure.
    Right, and I was planning to do so the day after vacuuming for that very reason. I could even feel noticeably reduced flow at the returns. However, the next day, pressure had dropped back from 21 PSI to 16 PSI, which was just 1.5 PSI higher than clean pressure (after adding DE).

    That said, today I noticed something else that could possibly be a contributing factor, but I don't know to what extent. I noticed a very slow leak just above the pump on the pressure side--just enough for a little water to run down the side of the pump after 30 minutes. I didn't have time to sit and watch how long it took for a drop to form, but the PVC threads were moist again in about 5 min after wiping them dry. While any leak, no matter how slow, obviously needs to be fixed, I wonder how much effect a leak that slow could have on filter pressure?
    ~18,000 gal (16x32)
    Hayward sand filter
    Circupool RJ45 SWG
    Hayward Max-Flo XL SP2305X7 pump (0.75 HP)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •